1. Field of Application
This invention relates to vibrating screens; and more particularly to vibrating screens with mechanisms for impacting against the underside of the screen deck to loosen and dislodge material which may have become stuck in the screen deck openings.
2. Description of the Prior Art
Vibrating screens are utilized to sift and separate bulk materials of varying characteristics for many applications. In general, these vibrating screens include a vibrating or live frame, suitably mounted on springs, and having a single screen deck, or a number of superimposed spaced screen decks. Each such screen deck is formed with an array of openings sized and spaced to provide the intended sorting and sifting of a type or types of bulk material. A vibrating mechanism is provided for vibrating the frame, screen decks, or decks, and bulk material, to effect the desired sifting and sorting.
Quite often the size or configuration of the apertures, and/or the nature of the bulk material to be sorted is such that the material tends to lodge in or clog up the screen openings. This is especially true for bulk material which may be wet due to processing requirements or inclement weather, or due to inherent sticky surface characteristics of the material.
Some available vibrating screens are equipped with screen unclogging or cleaning mechanisms which consist of a plurality of loose rubber balls disposed between the screen deck and a plate or tray positioned beneath the screen deck. However in such screens the requirement for the lower deck not only adds an additional cost but also provides a second and maybe unwanted level of screening that slows down the screening process. In addition in screens of the type shown in U.S. Pat. No. 2,946,440 of L. E. Simpson the balls have a tendency to migrate to one end of the apparatus when mounted at an angle as is often common for many vibrating screens; and thus to only provide the unclogging action at the lower most screen deck area. While in screens of the type shown in U.S. Pat. No. 2,269,289 of H. Schifflin et al the compartmentalization of the ball support deck, while acting to keep the balls positioned beneath the entire deck, should the screen be tilted, still displays a tendency for the balls to roll to the low end of each compartment, and necessitates the expenses of the compartmenting.
Other screens such as shown in U.S. Pat. No. 3,841,482 of J. B. Brown et al, and in U.S. Pat. No. 3,960,731 of L. K. Brandt, utilize a number of sliders of varying size and/or configuration disposed between the underside of the screen deck and a tray or deck positioned thereunder. Here again the slider support deck adds an extra cost and can interfere with the screening process. In addition the sliders tend to rub and abrade the underside of the screen deck and accelerate its wearing out and the cost of replacing same.
Another suggested approach to this problem entails the use of weighted elements supported for pendular type action beneath the screen deck. In mechanisms of this sort as suggested in U.S. Pat. No. 1,779,348 of A. W. Viehmann and in U.S. Pat. No. 3,070,230 of A. K. Peterson, the pivotal mounting of the weighted members is complicated and entails extra expense adding to the cost of the equipment; and is such that clogging of the pivotal mounting by the material being sorted will stop operation of unclogging mechanism. Those mechanisms which flex the screen to loosen clogged particles accelerate fatigue and cracking of the screen webs; while in those screens which merely allow the weighted ball to hang down below the screen support ribs, such as shown in U.S. Pat. No. 4,122,006 of E. Christensen et al, the relatively large arc of swing required for the ball may not be possible, or so reduces the impact force of the ball against the screen deck, as to render the unclogging action unsatisfactory.